New Delhi: A chilled glass of iced tea is considered one of the most refreshing and cooling drinks on a warm summer day.

However, now, a study has associated the beverage with cholera, saying that consuming iced tea and not always boiling drinking water may increase the risk of the disease in endemic countries.

Researchers revealed that during 2007-2010, Vietnam faced an increase in cases of the diarrheal disease, after a decade of declining cholera incidence.

Factors like drinking iced tea or unboiled water and having a water source near a toilet, increase the risk of contracting cholera in Ben Tre province of Vietnam.

Cholera is a bacterial disease causing severe diarrhoea and dehydration and its transmission is closely linked to inadequate access to clean water and is often spread through contaminated drinking water.

In the Ben Tre province of the Mekong Delta region in the southern part of Vietnam, no cholera cases were reported from 2005 until an outbreak in 2010.

In the new study, Thuong Vu Nguyen from the Pasteur Institute Ho Chi Minh City in Vietnam and colleagues interviewed 60 people who were confirmed to have been infected with cholera during the 2010 outbreak in Ben Tre.

Information about each person's eating and drinking behaviors and living environment was recorded.

The researchers also collected samples of nearby river water, drinking water, wastewater samples, and local seafood to test for Vibrio cholerae, the bacteria which spreads the disease.

The researchers found that drinking iced tea, not boiling drinking water, having a main water source near a toilet, living with other who have diarrhea and having little or no education were all associated with an increased risk of cholera, while drinking stored rainwater, eating cooked seafood or steamed vegetables were protective against the disease.

As much as 22 percent of people with cholera reported drinking iced tea in the week prior to their disease, whereas only three per cent of controls had drank iced tea in the week before being interviewed.

Patients with cholera were also more likely to always put ice in their water and to use sedimented river water for drinking, bathing, cooking, and brushing their teeth.

More work is needed to determine why iced tea boosts the risk of cholera, but the researchers hypothesise that the bacteria may be found in ice, which is often bought from street vendors.

"Along with traditional approaches that focus on enhancement of safe water, sanitation, and food safety, combined with periodic provision of oral cholera vaccines, a water quality monitoring system at ice-making plants should be established," they said.

The study was published in the journal PLOS Neglected Tropical Diseases.